The present invention relates generally to engine control systems, and more particularly to throttle position feedback controllers.
Many previously known motor vehicle throttle controls have a direct physical linkage between an accelerator pedal and the throttle body so that the throttle plate is pulled open by the accelerator cable as the driver presses the pedal. The direct mechanical linkage includes biasing that defaults the linkage to a reduced operating position, in a manner consistent with regulations. Nevertheless, such mechanisms are often simple and unable to adapt fuel consumption efficiency to changing traveling conditions, and add significant weight and components to the motor vehicle.
An alternate control for improving throttle control and the efficient introduction of fuel air mixtures into the engine cylinders is presented by electronic throttle controls. The electronic throttle control includes a throttle control unit that positions the throttle plate by an actuator controlled by a microprocessor based on the current operating state determined by sensors. The processors are often included as part of a powertrain electronic control that can adjust the fuel air intake and ignition in response to changing conditions of vehicle operation as well as operator control by driving springs that position the throttle valve.
Many electronic throttle control systems have position feedback controllers (see for example, U.S. Pat. No. 5,213,077/1993, U.S. Pat. No. 4,941,444/1990 and U.S. Pat No. 4,854,283/1989). Position feedback controllers or PID controllers (Proportional-Integral-Derivative) allow the control system to substantially maintain a setpoint by adjusting the control outputs. In an electronic throttle control system, the proportional and derivative elements position the throttle valve. The integration element primarily serves to drive system position error to zero. The higher the integral gain, the earlier the position error is driven out of the controller. However, position oscillation and integral windup limit integral gain. To clarify, system integrity is compromised with position oscillation because overshoot results. In addition, integrator windup occurs when the feedback controller exceeds the saturation limits of the system actuator and is unable to immediately respond to changes in the position error. That is, with windup, the position feedback controller exhibits lengthy settling times.
Many modern electronic throttle control systems use integration increments, generated by the integration elements, that are proportional to position error to drive out position error. However, this limits integral gain for small position error and allows position error to affect the system for a longer period of time and consequently decreases efficiency.
Many modern electronic throttle control systems also have their integration increment operating substantially continuously. This operation is inefficient because when the throttle is moving, the proportional and derivative terms of the position feedback controller position the throttle. Therefore, having the integrator active is wasted effort because the integrator will tend to wind up, and position error may occur when the integrator is then forced to unwind. Furthermore, when the throttle receives a new position command, the integrator winds up while the throttle is going to the new position and subsequently must wind down once the new position is attained. This unwinding sacrifices performance. In addition, when the throttle mechanism encounters an obstruction to operation (e.g. ice on the throttle valve), the integrator will tend to wind up and then, when a non-obstructed position is commanded, the integrator term unwinds and large position errors may result.
The disadvantages associated with these conventional position feedback controller techniques have made it apparent that a new technique for position feedback control is needed. The new technique should have minimal position oscillation and minimal integral windup and should also have a high integral gain. The present invention is directed to these ends.
It is an object of the present invention to provide an improved position feedback controller. It is also an object of the present invention to provide an improved position feedback controller for an electronic throttle control system.
In accordance with the present invention, an electronic throttle control system including a throttle valve for adjusting the amount of air drawn into the engine is disclosed. The throttle valve is controlled by a throttle position feedback controller which is adapted to suspend an integration element when position error absolute value is greater than a threshold, or when the position rate absolute value is greater than another threshold. The integration element includes an integration increment such that generation of the integration increment begins by a determination made of the position error between the throttle position and the position command. Once a determination of the sign of position error is made, a gain is applied to the position error. Also, a gain is applied to the sign of position error. The integration element of the throttle position feedback controller then operates with the position error and the sign of position error. The throttle valve then reacts in response to the throttle position feedback controller.
Additional advantages and features of the present invention will become apparent from the description that follows and may be realized by the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.